1. Field
The present disclosure relates to techniques for communicating optical signals. More specifically, the present disclosure relates to a low-power, broadband optical switch that is electrostatically actuated.
2. Related Art
Silicon photonics is a promising technology that can provide large communication bandwidth and low power consumption needed to facilitate inter- and intra-chip interconnections. For example, a point-to-point communication network can be established using silicon-photonic devices and links to interconnect a large number of processor cores in a manner that achieves scalable performance with affordable manufacturing and energy costs.
One of the building blocks in inter- and intra-chip silicon-photonic interconnects is a silicon-waveguide optical switch. The silicon-waveguide optical switch enables an optical signal, or bundles of optical signals, to be selectively redirected from one optical waveguide to another. Consequently, the silicon-waveguide optical switch can play an important role in facilitating reconfigurable networks and interconnects, as well as in providing dynamic bandwidth provisioning. This component is particularly useful in circuit-switching architectures.
In large-scale, wavelength-division multiplexing (WDM) optical networks or interconnects, the number of optical switches can be enormous. Therefore, it is desirable for these optical switches to have: low power consumption, low optical loss, a high ON/OFF extinction ratio (ER), and a compact size.
Also, because multiple wavelength channels may be switched simultaneously, broadband optical switches are often needed. A variety of techniques have been proposed to implement a broadband optical switch. These techniques include mechanical actuation, such as in a microelectromechanical system (MEMS). For example, using MEMS, an optical fiber can be physically shifted to drive an optical signal onto one or more additional optical fibers.
Other techniques have been used to implement a broadband optical switch including techniques that take advantage of: electro-optic effects, magneto-optic effects, and thermal-optic effects. For example, a Mach-Zehnder interferometer (MZI) has been used to build 1×2 and 2×2 broadband, silicon-waveguide optical switches, using either the thermal-optic effect or an electro-optic effect (such as carrier injection or carrier depletion) during switching. In a typical MZI silicon-waveguide optical switch that is based on thermal-optic switching, a thermal phase tuner (such as a heater) is integrated into one ‘arm’ of an MZI to adjust its phase relative to the other reference ‘arm.’ In this way, the thermal phase tuner controls the output light intensity induced by the interference of light in the two arms. Similarly, in a typical MZI silicon-waveguide optical switch that is based on electro-optic switching, an electro-optical phase tuner uses carrier injection or carrier depletion to adjust the relative phase. This can increase the switching speed, at the cost of higher insertion loss associated with carrier absorption.
Note that because of the relatively small dependence of index-of-refraction in silicon on temperature or applied voltage, MZI silicon-waveguide optical switches are typically large (with lengths of several millimeters), and have significant power consumption. Because these characteristics are sub-optimal for inter- or intra-chip interconnects, to date these optical switches have typically been used in telecommunications.
In order to reduce the size of MZI silicon-waveguide optical switches, a ring-resonator silicon-waveguide optical switch has been proposed, using either the thermal-optic effect or the electro-optic effect during switching. By using ring resonators, the size of the optical switch can be a couple of orders smaller than those that include an MZI. However, ring resonators are usually very sensitive to wavelength. Consequently, optical switches that include ring-resonators are typically wavelength selective or very narrow band.
While the periodic resonances of the ring resonators can offer pseudo-broadband capability, tuning is typically needed to overcome the resonance shifts associated with manufacturing tolerances and changes in the ambient temperature. The sensitivity to changes in the ambient temperature can, at least in part, be addressed by a high-order ring-resonator optical switch that includes multiple coupled ring resonators. However, this approach often cannot tolerate the resonance shift associated with manufacturing tolerances, which can be as large as tens of nanometers. In addition, optical switches with multiple-coupled ring resonators are larger, and have higher tuning and switching power consumption than optical switches with a single ring resonator.
Hence, what is needed is a broadband optical switch without the above-described problems.